Facing an AR receiver. Does it matter?

357Max

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    Another thread on the same/sim subject inspired me to try putting it to the test.
    Link here to other thread. https://www.snipershide.com/shooting/threads/facing-ar-15-receiver.7133119/

    Since I was about to build an 18" 223 Wylde on quality parts I figured it'd be a good test bed to maybe shed some light on this.

    I've been kind of agnostic as too how much difference it'd really make when using quality parts. Despite that I'll admit to having lapped every build I've done.
    Not only have I lapped every build, but also shimmed or bed set every barrel extension to the receivers. Tight or thermal fits in BCM receivers still get slid in with a light coat of 620 Loctite. Loose fits get SS .001 shim stock + 620.

    So here's the plan.
    Part A (Complete as of 8/6)​
    • Build the gun using high quality parts without facing or shimming the extension.
    • Break it in (i.e. tune gas, zero scope).
    • Shoot groups with various brands of factory 77gr match ammo.
    Part B​
    • Tear gun back down, lap receiver face, shim/bed extension to receiver, & reassemble with no other changes.
    • Re shoot groups with same brands/lots of 77gr Ammo
    I got a deal on a barrel (4th of July sale) so decided to build a gun around it. Purpose is to shoot PRS style IWI & Geissele gas gun matches.

    Build list:

    Upper.
    VLTOR Mur-1 upper that's unmodified. Accushim added to upper for a slight drag fit of rear take down pin.
    Mega Wedge lock 12-5/8" rail that I had to mill out the front of (I know sacrilege)
    Proof Carbon 18" 223W 8T. Gas system is .815 dia & 5/8" shorter than RL so intermediate I guess. The gas block is Iron, pick rail on top, fully adjustable, keyed to barrel, retained with a nut, & straight gas tube attaches via flared compression fitting like a brake line
    SRC low mass BCG - Head space was Go +.002
    Geissele Airborne CH
    Precision armament Hypertap brake
    Area 419 Keymod Arca rail (I also had to mill this to fit)
    Topping it off will be a MPA 1.25 x 34mm mount & an XTR 3 3.3-18 SCR-2 mil.

    Lower
    Std Forged Lower machined for Ambi bolt catch (Teal Blue Bravo catch)
    AR Gold trigger set +-2.5lbs
    BCM mod 3 grip
    VLTOR EMOD stock with the RE10/A5SR extension & A5 buffer/spring setup.

    For part A test
    VLTOR MUR-1 upper receiver face unmodified & barrel extension was pretty loose. Barrel just torqued 60 ft lbs dry fit.
    IMG_7113.jpg


    As detailed in the build list above, this barrel is and oddball. It was a run Proof did for the Savage MSR competition rifle. As of 2022 Savage has, without any notification removed all AR platforms or even mention of them from their catalog.

    Thanks to their Woke-mess & the likely lack luster sales for the $3000 MSR I got a great deal on the barrel from Stockey's. It included the Steel Gas block, gas tube, & a really ugly 2 port brake.
    Unfortunately the Savage handguards for this rifle were probably all burned in a fire pit to pledge some sort of Woke allegiance BS.
    The gas system is 1" short of rifle length & combined with the pic rail gas block, limits handguard length to about 10.5".
    There's a lot to like with this barrel. Profile is IMO pretty close to ideal for a Carbon 223 with the .815 gas block size, the threaded/keyed block retention, and the flared straight gas tube. I liked it enough to offset the PITA it would be to fit a handguard. Plus I already had the 12-5/8" Mega wedge lock (keymod) & the Area 419 Keymod Arca rail.

    Pictured below is this barrel on end next to a proof steel 20" with rifle length gas. Also a pic showing gas block/gas tube - handguard fitting.
    IMG_7109.jpg
    IMG_7107.jpg

    Did the usual tricks. Bolt extractor & ejector removed to check head space. Rounded the ejector & deburred the extractor. Not pictured but check & blend M4 feed ramps as necessary (they matched really well on this one).

    IMG_7112.jpg
    IMG_7125.jpg


    Yeah I chopped a Mega wedge lock. At least it was a key mod I chopped on. Insured clearance all the way around this bastard gas system to handguard. Even had to cut the bottom back of the LWRC front sight to clear. I like the look, it was worth the effort to me.

    IMG_7140.jpg


    Just need to get a taller scope mount so the rear buis will fit.
    IMG_7141.jpg
     

    357Max

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    Part A first groups.

    Factory 77gr Ammo used.

    Break in sidebar: When I say break in it means adjusting gas & that's about it.

    I think "Barrel brake in" for a quality single point cut & lapped barrel is hogwash! If it's right it needs a couple patches and then let it rip.

    The above is exactly what I did. Few patches & off to the range with no cleaning gear.

    I was short on time for the range today.
    Started with Winchester 55gr bulk 5.56 FMJ. Shot at paper @ 50y, missed paper, burned 1 at a leaf in the middle of the berm, up 10mils & right 1, then hit leaf. Added 2 clicks gas & shot paper. The bulk 55gr group @ 50 was pretty bad.
    Total of 23 rounds Win 55gr shot at 50y berm.

    Moved to 100y & shot 5 x 77gr PMC at a 3" target. Adjusted scope & shot 5 more.

    Then shot the below 6 x 5 target. The target was shot left to right top & then same for bottom. The only malfunction I had was on the last bull (bottom right). I think the Sig 223 77gr is slow or at least makes way less gas then anything else. It didn't lock the bolt back on the first group (top right), but I didn't want to add gas in the middle of the 6 x 5. So the bottom right bull I had 2 short strokes and had to come off the gun Twice.

    This was shot off a stupid T bench. Whoever came up with that bench design should get punched in the dick. Arms hanging off both sides.
    I also realized today that I'm going to need a flat rear squeeze bag for the Emod stock. The foot on this stock is really small so the round rear bag wasn't ideal.

    Rounds 33-63 shot on 6 x 5. Barrel is broke in now.
    I'll tear it down tomorrow. After the next 6 x 5 I'll get some speeds.

    IMG_7143.jpg
     

    Oryx

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    Just a suggestion, But if you are going to test for a variable, don't try to introduce multiple changes and try to draw inferences back to a single variable.

    For instance if you are testing for the facing of a receiver, don't try to add in shimming and bedding the receiver extension at the same time. How are you going to separate the impacts of each in your results?
     
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    srt-4_uk

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    Unfortunately the Savage handguards for this rifle were probably all burned in a fire pit to pledge some sort of Woke allegiance BS.
    The handguard bolted directly to the odd reciever. So even if they had any, it wouldn't work with a normal upper

     
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    357Max

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    Just a suggestion, But if you are going to test for a variable, don't try to introduce multiple changes and try to draw inferences back to a single variable.

    For instance if you are testing for the facing of a receiver, don't try to add in shimming and bedding the receiver extension at the same time. How are you going to separate the impacts of each in your results?
    You are correct & that’s been bugging me a little.
    I could have used a BCM thermal upper & that would have left only receiver facing. I suspect loose receiver fit has a bigger effect. Since I went with the Vltor both are in play.

    Problem is Time. I’m not retired. Busy as hell & traveling for work the next 5 weeks. Let me think about this. Might just face the receiver today and reshoot next weekend as you suggested. Then repeat following week after shimming extension. The results would certainly be more beneficial if I isolate the 2 variables.

    I was surprised how well it shot the factory loads & lack of POI shift across 3 different 77 loads. It’s been over a year since I shot 223. Damn this this is soft shooting.

    I’m just impatient & want to get to hand loading for it asap.
     
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    357Max

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    The handguard bolted directly to the odd reciever. So even if they had any, it wouldn't work with a normal upper

    Yep I hadn’t seen that. Actually looks like a good receiver set up.
    BE65C2C3-2C8B-420F-AFD3-DDD62FC27CA1.jpeg
     

    Oryx

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    You are correct & that’s been bugging me a little.
    I could have used a BCM thermal upper & that would have left only receiver facing. I suspect loose receiver fit has a bigger effect. Since I went with the Vltor both are in play.

    Problem is Time. I’m not retired. Busy as hell & traveling for work the next 5 weeks. Let me think about this. Might just face the receiver today and reshoot next weekend as you suggested. Then repeat following week after shimming extension. The results would certainly be more beneficial if I isolate the 2 variables.

    I was surprised how well it shot the factory loads & lack of POI shift across 3 different 77 loads. It’s been over a year since I shot 223. Damn this this is soft shooting.

    I’m just impatient & want to get to hand loading for it asap.
    I definitely understand the time crunch.

    If it were me I'd start with the barrel extension to receiver fit first and then move to the facing ... just me .... but it's your experiment
     

    Middle Man

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    Thanks to their Woke-mess & the likely lack luster sales for the $3000 MSR I got a great deal on the barrel from Stockey's. It included the Steel Gas block, gas tube, & a really ugly 2 port brake.
    Unfortunately the Savage handguards for this rifle were probably all burned in a fire pit to pledge some sort of Woke allegiance BS.
    Nicely put together.

    Likely more due to the Savage MSR's total failure in the marketplace and many cancelled purchase orders. Some MSR's still sitting around at wholesale and retail. Ditto, Savage's pistol effort (re-tooled Honor Defense).
     

    Butterburger

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    many will tell you it is not necessary. I will tell you it is cheap insurance. Hell I just did a mur upper receiver and lapping the face will tell the tale. It was not square.

    For a precision upper I would definitely do it. When it comes time to time the barrel nut and the gas tube and get the barrel nut torque where you want it lapping is your friend.
     

    jhr1986

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    Thanks for sharing your results, I look forward to seeing the final outcome.

    Will you be using one of the various lapping tools (like this one) or turning it on a lathe/mill?
     

    357Max

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    Thanks for sharing your results, I look forward to seeing the final outcome.

    Will you be using one of the various lapping tools (like this one) or turning it on a lathe/mill?
    I used the Brownell’s lapping tool with the receiver upside down and horizontal. About to find out headed to the range now.
     

    ZA206

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    I just lapped and bedded several of my AR rifles. Haven’t really shot any for groups but did rezero every rifle. The thermal fit ones may have moved 1 MOA. There was a 6.8 hunting rifle (had to take off a bunch of metal to get it squared up and the barrel fit was loose)…. When I re-zeroed that rifle, it was probably 10-15 MOA off…. I wasn’t even on the sight in board at 50 yards! Crazy.

    I always had issues with it not grouping… it was a 1” rifle at its best with a quality WOA barrel. I’m sure it’s MUCH MUCH better now. Need to check it.
     

    Oryx

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    I just lapped and bedded several of my AR rifles. Haven’t really shot any for groups but did rezero every rifle. The thermal fit ones may have moved 1 MOA. There was a 6.8 hunting rifle (had to take off a bunch of metal to get it squared up and the barrel fit was loose)…. When I re-zeroed that rifle, it was probably 10-15 MOA off…. I wasn’t even on the sight in board at 50 yards! Crazy.

    I always had issues with it not grouping… it was a 1” rifle at its best with a quality WOA barrel. I’m sure it’s MUCH MUCH better now. Need to check it.
    How did you go about measuring the relationship between the face of the receiver and the bore to determine the it was "squared up" after removing a bunch of metal? You removed so much metal that it was off 10-15 MOA at 50 yd ? not sure how that would give you the confidence that it is "MUCH MUCH better now"
     

    ZA206

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    How did you go about measuring the relationship between the face of the receiver and the bore to determine the it was "squared up" after removing a bunch of metal? You removed so much metal that it was off 10-15 MOA at 50 yd ? not sure how that would give you the confidence that it is "MUCH MUCH better now"
    I used the Brownells tool. Some of my uppers just needed a little lapping, some needed basically none. This one was an outlier, it took me a while to get it square. TBH, I think the barrel must have been canted or something by the the receiver face being so “unsquare”. It’s been a long time since I mounted and zeroed that scope on that rifle, but IIRC it needed a ton of adjustment (more that what I’d call “normal”) zeroing it. I had always assumed it was the scope mount or somethin.

    BTW, I never removed the scope or the scope Mount when I lapped that upper, so it wasn’t a scope issue.

    ZA
     

    357Max

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    Spoiler alert, the damn thing shot better when I slapped it together. Hell .621” avg for a 6x5 with 3 different factory loads would be pretty hard to beat & it didn’t.

    So when I went to lap it, to my surprise it was the squarest VLTOR I’ve lapped. It was also the only gen 1 VLTOR I ever built.
    AF4BD12E-15B5-4BB0-8371-CCFBB6AC8EC2.jpeg
    EDBA4710-1734-453C-817D-EE434237BC31.jpeg


    Since it cleaned up so quickly I went ahead and shimmed the extension also. It was loose & took a full wrap of .001 shim + Locktite 620. That gave it a tight fit that I was able to get within about 1/4” from fully seated before having to tap the last bit with a rubber mallet. If you look close at the image showing extension and ramps the edge of shim & a little 620 is just barely visible.
    1E038927-F2DA-4143-9E8F-A6E6398FEE90.jpeg
    531468FC-78B2-42B1-B775-189E543F760E.jpeg
    E1CDE1F0-9A9D-4570-AE26-0C25FCC7F532.jpeg


    Everything else was the same with 1 exception. The Geissele airbore charging handle was binding so I swapped it for a known good geissele super CH.

    Didn’t even add gas since I wanted to be the same.
    Same shitty bench, same bag & bipod. Same 20rd pmag. Same ammo lot shot in same order. Same round count from clean barrel. 23 x 55fmj, 10 x 77 xtac, & then 6 x 5. No out takes or do overs.
    I did need .3 mil rt. & .1 up to get same POI, but scope was also R&R’d.
    Some of the inconsistency was surely me as I wasn’t super settled in. The last 2 groups bottom right I was pretty consistent (loose hold). The gun shoots well with all 3 brands of 77 that varied 200fps.

    After the 6 x 5 I ran all three loads over the Magneto V3
    PMC 223 X-Tac 77 = 2551 avg SD 22.2
    IMI Razor Core 5.56 77 = 2706 avg SD 25.5
    Sig Elite 223 77 = 2509 avg SD 16.0

    Left the Magneto on and ran 5 Of the IMI @500y 10” plate. It held a 1 moa group, but I suspect the large SD is just starting to show at 500. At 700+ I’ll want hand loads with hopefully sub 10 for SD.

    The test wasn’t great. A rest would make sense for something like this, but I don’t own one. I shoot bi-pod bag or positional bag.

    My take away is that with Quality parts & 60+lbs barrel nut torque combined with a free floated rail. Lapping and shimming doesn’t do much.

    Looking forward to putting some of my own loads through this.

    94259D0C-3D0D-4FE7-83C2-3D9992B19B87.jpeg

    DE3B56F0-5A3D-4777-92BC-E7A121B127A9.jpeg
     

    iktomi

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    Spoiler alert, the damn thing shot better when I slapped it together. Hell .621” avg for a 6x5 with 3 different factory loads would be pretty hard to beat & it didn’t.

    So when I went to lap it, to my surprise it was the squarest VLTOR I’ve lapped. It was also the only gen 1 VLTOR I ever built.
    View attachment 7933499View attachment 7933500

    Since it cleaned up so quickly I went ahead and shimmed the extension also. It was loose & took a full wrap of .001 shim + Locktite 620. That gave it a tight fit that I was able to get within about 1/4” from fully seated before having to tap the last bit with a rubber mallet. If you look close at the image showing extension and ramps the edge of shim & a little 620 is just barely visible.
    View attachment 7933501View attachment 7933502View attachment 7933503

    Everything else was the same with 1 exception. The Geissele airbore charging handle was binding so I swapped it for a known good geissele super CH.

    Didn’t even add gas since I wanted to be the same.
    Same shitty bench, same bag & bipod. Same 20rd pmag. Same ammo lot shot in same order. Same round count from clean barrel. 23 x 55fmj, 10 x 77 xtac, & then 6 x 5. No out takes or do overs.
    I did need .3 mil rt. & .1 up to get same POI, but scope was also R&R’d.
    Some of the inconsistency was surely me as I wasn’t super settled in. The last 2 groups bottom right I was pretty consistent (loose hold). The gun shoots well with all 3 brands of 77 that varied 200fps.

    After the 6 x 5 I ran all three loads over the Magneto V3
    PMC 223 X-Tac 77 = 2551 avg SD 22.2
    IMI Razor Core 5.56 77 = 2706 avg SD 25.5
    Sig Elite 223 77 = 2509 avg SD 16.0

    Left the Magneto on and ran 5 Of the IMI @500y 10” plate. It held a 1 moa group, but I suspect the large SD is just starting to show at 500. At 700+ I’ll want hand loads with hopefully sub 10 for SD.

    The test wasn’t great. A rest would make sense for something like this, but I don’t own one. I shoot bi-pod bag or positional bag.

    My take away is that with Quality parts & 60+lbs barrel nut torque combined with a free floated rail. Lapping and shimming doesn’t do much.

    Looking forward to putting some of my own loads through this.

    View attachment 7933539
    View attachment 7933540
    FWIW, I usually find that IMI 77 has a flier or two per box of 20. Shot my lot before attempting to diagnose it. (Concentricity maybe?) Would buy by the case again, if it ever shows up through my regular vendors. (By flier, I mean unexpected POI compared to whatever I see through the glass, feel through the position.)
     

    357Max

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    60 ftlb+ on the barrel nut? Why?

    Hard to tell if that is sarcasm? Or a genuine question?

    Sarcastic answer first.
    60 ftlbs is the magic torque that makes an unlapped unbedded Small frame AR shoot sub 3/4 minute 6x5 using 3 different factory loads.

    Also 65 ftlbs is what is called for on that wedge lock rail.
     

    357Max

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    This magic torque number is based on what? I have never seen it mentioned or touted.

    There is no magic torque spec.

    For an AR barrel there are some known good torque specs for specific barrel profiles using std barrel nuts.

    The right answer for starting torque can vary depending on parts.
    My AR’s all have either steel or titanium barrel nuts, but there are also aluminum options.

    The Mega Wedge lock rail on this build uses a steel nut & they recommend 65ft lbs. I just checked my Snap On torque wrench & I actually used 62ft lbs both times.

    If for example; if this was an aluminum barrel nut with a 40 lb spec that loose fitting extension might have been moving & not shot nearly as precise.

    Torque is doing 2 things.

    1. Holding the extension tight to the receiver.
    A. If torque is high enough it will pin the extension tight to receiver face. If face is a little out of square it will attempt to square it by taking up any slop in extension to receiver fit. What matters is that it stays pinned in the same place shot to shot.

    What is enough depends on the strength of the barrel nut, quality of the threading, and length + weight of barrel. A lot of torque is required just to overcome the friction of the threads. The larger diameter the higher the friction. For a thread this big 60ft lbs isn’t much. It’s the yield strength Of the 7075 receiver threads that cap the clamping capability on an AR.

    2. Torque affects barrel harmonics. Changing torque can/does change the tune on the barrel similar to a tuner.

    So in the lapping shimming experiment I did I made a more rigid upper & in doing so also changed harmonics. Might have actually hurt it. Hell it might like 50ft lbs or 70 now.

    Here’s a video that gets into barrel torque & harmonics at about the 6 minute mark.

     
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    Vynz

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    What is enough depends on the strength of the barrel nut, quality of the threading, and length + weight of barrel. A lot of torque is required just to overcome the friction of the threads. The larger diameter the higher the friction. For a thread this big 60ft lbs isn’t much. It’s the yield strength Of the 7075 receiver threads that cap the clamping capability on an AR.

    For uppers where the barrel nut/receiver relationship is reversed like the Aero Enhanced, Seekins, JP, Mega uppers; do you think the torque required is more/less or as important as it is for standard receivers?
     

    6.5SH

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    All of the Joe Carlos videos are worth watching. A real wealth of information there.
     

    357Max

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    For uppers where the barrel nut/receiver relationship is reversed like the Aero Enhanced, Seekins, JP, Mega uppers; do you think the torque required is more/less or as important as it is for standard receivers?

    All the same still applies. Doesn’t really matter if the nut has female threads (traditional) or male threads like Aero enhanced. It still has to clamp the very thin rim of the extension to the receiver face with enough force to stay put while a 16-22” lever is hanging off the end.

    The enhanced receivers are Just taking the hand guard connection off the barrel nut & adding strength to the receiver hand guard connection to prevent force applied to the hand guard from causing POI shifts.
     

    supercorndogs

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    60 ftlbs is the magic torque that makes an unlapped unbedded Small frame AR shoot sub 3/4 minute 6x5 using 3 different factory loads.
    There is no magic torque spec.

    My take away is that with Quality parts & 60+lbs barrel nut torque combined with a free floated rail. Lapping and shimming doesn’t do much.
    I asked because I wanted to know how you drew your conclusion. There is in fact a magic torque number, but the only way to find it is to experiment. 60-80 always seems like a lot to me based one the aluminum receiver threads, and also based on my I-beam torque wrench and seeing ears on barrel nuts let go around 60 trying to line up gas tubes.

    I asked because I don't see anything about tuning torque. In the video he says to start with 60ftlbs on as A2 profile barrel, and 47ftlbs on a heavy profile barrel. Then you experiment with different torque specs. He also says tuning barrel nut torques doesn't work as well if the extension to receiver clearance is not tight.

    Did you torque the barrel nut wet or dry? If you went together dry, then got some lube on your threads after facing. Your tune could easily change because your barrel nut torque. I.E 60ftlbs is considerably more torque on a wet thread vs a dry thread.

    Also having calibrated torque wrenches, I can tell you most people couldn't hit a torque number consistently on a click style wrench. When I say most people, I mean I have never seen a new person try to pass torque wrench calibration, whom it didn't take 20 or 30 try to get it to click at the same torque 3 times in a row to pass the calibration test.

    I dont think your experiment provided enough information to draw the conclusion you did.
     
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    Earnhardt

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    Your experiment did provide enough info to draw the conclusion you did...

    Thanks!
     

    357Max

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    I asked because I wanted to know how you drew your conclusion. There is in fact a magic torque number, but the only way to find it is to experiment. 60-80 always seems like a lot to me based one the aluminum receiver threads, and also based on my I-beam torque wrench and seeing ears on barrel nuts let go around 60 trying to line up gas tubes.

    I asked because I don't see anything about tuning torque. In the video he says to start with 60ftlbs on as A2 profile barrel, and 47ftlbs on a heavy profile barrel. Then you experiment with different torque specs. He also says tuning barrel nut torques doesn't work as well if the extension to receiver fit is not tightened up first.

    Did you torque the barrel nut wet or dry? If you went together dry, then got some lube on your threads after facing. Your tune could easily change because your barrel nut torque. I.E 60ftlbs is considerably more torque on a wet thread vs a dry thread.

    Also having calibrated torque wrenches, I can tell you most people couldn't hit a torque number consistently on a click style wrench. When I say most people, I mean I have never seen a new person try to pass torque wrench calibration, whom it didn't take 20 or 30 try to get it to click at the same torque 3 times in a row to pass the calibration test.

    I dont think your experiment provided enough information to draw the conclusion you did.

    You can’t deny how well this thing shot on the first 6x5 with just proper assembly.

    I am satisfied with my conclusion & that’s why I did it. By all means run your own test. Hope you prove me wrong.

    No doubt a better test could be run. It would take more rounds, a repeatable rest, and only make 1 change at a time. I don’t get payed for this & my time comes at a premium these days.

    In my case, either I couldn’t shoot the difference, couldn’t shoot consistently enough, the next box of ammo (same lot) might not have been as good, or it changed harmonics for the worse with this ammo. It wasn’t even gassed optimally, but I wanted both 6x5’s the same. Even if it did hurt it harmonically with these loads, it may have improved it’s potential for a tuned load.

    It is kind of noteworthy that it shot the Sig the worst on the first 6x5 & the Sig shot the best on the second 6x5.

    As for torque, I’ve got far more experience than most. I have had formal accredited training along with many years of daily practical experience. I have top quality torque wrenches that have been sent in for calibration checks. Also have torque angle gauges & bolt stretch gauges. I’ve without exaggeration, torqued tens of thousands of critical fasteners. Those included torque to stretch, to yield, & to angle. Some also required safety wire, retention tabs, & other application specific retention methods. There is no short cut to experience and there’s a lot more to it than setting a wrench and pulling till it clicks. That’s the dumb part. Guns are pretty basic and low tech compared to the strenuous loads & harmonics fasteners are subjected to in racing engines.

    I’ve done my own experimenting with different lubricants over the years. More than I can remember. ARP, Oliver, Crane, Crower, Comp Cams, Isky, Redline, Royal Purple , Polymer Dynamics, Calico, MKZ etc etc.

    For gun assembly I use Redline assembly lube & PolyDyne 2A gun lube.

    I used the Redline Petroleum based assembly lube on both the receiver threads and the nut, both times. Torqued in steps both times (35 then 62).

    I chose 62lbs for several reasons.
    1. From memory every time I’ve read about someone experimenting with barrel nut torque they’ve landed between 55- 65 as optimal (steel nuts & med heavy barrel profiles).
    2. This is a steel nut. There is no gas tube timing required.
    3. The manufacturers recommended torque was 65lbs
    4. I wanted to give it the best chance of success when unlapped & not shimmed. Had I started at 35lbs the loose extension fit may have been able to move.

    I posted the Joe Carlos video to provide some of the rational behind it. That said it’s a bit of a different deal. He’s working within specific rules, parts selection and ammo lots. His statement about first ensuring a tight extension fit is logical. Without a tight fit your chasing 2 variables. I’m not going to screw with trying to tune barrel nut torque. I can simply choose a different part, load my own ammo, or throw a tuner on if I choose.

    Can varied torque change harmonics? I think so sure, but I can also tune the load. My goal is not to tune the gun to factory ammo. I’ve done that and it’s a pain in the ass. Personally I’d rather build as solid a platform as possible and then work the load to bring it in tune. Based on my experience I believe 62lbs will maintain a consistent clamp load on the barrel & that’s all I wanted in this case.

    The gun is telling me it can shoot very well weather lapped/shimmed or not given quality parts and adequate torque loads.
     

    StaveyIL

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    If you have to max out your iron sights . You probably should have faced it.
     

    supercorndogs

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    If mine shot that well on the first assembly. I would not have taken it apart to shim it and lap it.

    I may tighten up the barrel nut and see if the groups tighten up.

    I am not trying to prove you wrong. Your target already proved to you what you needed it to, thats the end goal. I was just thinking through the endless amount of variables in trying to run a decent experiment like this.

    Mine is not shooting well enough that I am going to leave it alone. I am going to try a different bullet before I do anything else though.
     
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    supercorndogs

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    If you have to max out your iron sights . You probably should have faced it.
    Your handgaurd could also not be straight or could be out time a little, or a crooked barrel. Those are other things that put irons at end range anyway.
     

    StaveyIL

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    I just noticed this thread and it just so happens, I recently seen this happen.
    I honestly don’t care what others do. I just know as a fact this does occur.
     

    rpoL98

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    Everything else was the same with 1 exception. The Geissele airbore charging handle was binding so I swapped it for a known good geissele super CH.

    Didn’t even add gas since I wanted to be the same.
    Same shitty bench, same bag & bipod. Same 20rd pmag. Same ammo lot shot in same order. Same round count from clean barrel. 23 x 55fmj, 10 x 77 xtac, & then 6 x 5. No out takes or do overs.
    I did need .3 mil rt. & .1 up to get same POI, but scope was also R&R’d.
    ...
    it's too bad you replaced the scope for the "after" test, would've been interesting if the original scope POI shifted.
     

    357Max

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    it's too bad you replaced the scope for the "after" test, would've been interesting if the original scope POI shifted.
    Yeah it just would’ve been a royal pain to leave it mounted to the bare upper while lapping etc. The scope never came out of the mount. This is the first MPA mount I’ve used so not sure how repeatable they are. FWIW I put it back in same spot on rail & torqued it the same.
     

    rpoL98

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    Spoiler alert, the damn thing shot better when I slapped it together. Hell .621” avg for a 6x5 with 3 different factory loads would be pretty hard to beat & it didn’t.

    ...
    I did need .3 mil rt. & .1 up to get same POI, but scope was also R&R’d.
    ...
    i misunderstood, I thought you changed the scope, scope mount. couldn't see the forest for the trees, lost the thread of the thread.

    so then the .3 mil azimuth, and .1 mil elevation was hopefully an improvement in the alignment of the barrel bore axis with the receiver bore axis (main benefit of receiver face lapping). But I guess, only with iron sights would you be able to tell if there is better alignment, or if you actually went more askew.
     
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